1. Field of the Invention
The subject invention relates to magnetic recording and, more particularly, to the magnetic recording of images with the assistance of thermal image patterns.
2. Description of the Prior Art
Magnetic imaging has been the subject of serious investigation in recent years, since it has several advantages over more conventional imaging techniques.
For instance, magnetic imaging offers the prospect of an avoidance of time-consuming and delicate chemical processing steps now required in customary photography. Magnetic imaging also offers the prospect of an avoidance of expensive and potentially dangerous high-voltage equipment now required in certain types of electrostatic xerography machines. Moreover, magnetic imaging techniques provide a record that is free of the decay encountered with electrostatic images and that can be printed out in large numbers without the need of reimaging between printouts.
Thanks to extensive efforts in this area, magnetic imaging techniques are becoming comparable in terms of light sensitivity and exposure speed with electrostatic xerography and with conventional photographic methods.
As a common denominator, these advanced magnetic imaging techniques employ a magnetic image recording medium susceptible to an image-wise change of magnetization in response to thermal image patterns. In some instances, the requisite thermal image pattern can be provided by a high-energy flash of light acting by way of a master image. Other situations, such as those wherein a high-intensity flash of light would damage the master image or would not be transmitted or reflected with sufficient intensity, require a thermal image pattern generating device which provides the requisite thermal image patterns in response to image-wise exposures.
An early attempt at such thermal image generating devices may be seen in U.S. Pat. Nos. 2,798,559 and 2,798,560 by A. J. Moncrieff-Yeates, issued July 9, 1957. That proposal overlooked the then still little known effect of thermoremanent magnetization and, accordingly, has found no commercial application in the better than 20 years of its existence. More recent developments have produced acceptable images, but are rather costly in their implementation. While this would still be satisfactory in the case of professional equipment or even in the case of heavily used commercial machines, there exists a need for low and medium priced magnetic copying, duplicating and other imaging methods and apparatus providing an image quality comparable to the potentially more expensive techniques.
In solving the underlying problem and in satisfying this need, the subject invention provides magnetic imaging methods and techniques which may also advantageously be employed in the context of high-grade professional and firstline commercial equipment.
A major drawback of even the most advanced prior-art magnetic imaging equipment resides in the fact that the image transducer they require, that is the device which provides thermal image patterns in response to image-wise exposures, approaches and, in some cases, even exceeds the capabilities of present-day technology in terms of energy requirements, resistance to thermal shock or deterioration, and fidelity and purity of reproduction. The effects of thermal transducer imperfections on the resulting magnetic image are particularly cumbersome and require considerable effort and expense for their elimination.
That prior-art efforts which have dealt with similar areas offer no solution may be seen from U.S. Pat. Nos. 2,914,403 by M. L. Sugarman, issued Nov. 24, 1959, 3,307,034, by L. F. Bean, issued Feb. 28, 1967, 3,424,579, by A. Balint et al, issued Jan. 28, 1969, 3,533,784, by D. B. Granzow et al, issued Oct. 13, 1970, 3,535,036, by G. K. Starkweather, issued Oct. 20, 1970, and 3,555,557, by G. R. Nacci, issued Jan. 12, 1971.